(1) First Problem
Conventionally, there has been provided in a press brake a workpiece positioning device as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-7938, and this workpiece positioning device includes a sensor at the central portion on the abutting face of a back gauge and an electromagnet on both sides of this abutting face.
Owing to such construction, when a workpiece is abutted against mentioned sensor, by the electromagnets being excited, this workpiece is sucked and secured, thereafter when a ram is driven, thus a punch and a die come close to each other, and the punch is contacted with the workpiece (pinching point), the electromagnets are demagnetized to release the workpiece, and then this workpiece is subjected to a predetermined machining with the punch and the die.
Recently, job shop type production becomes mainstream, and the shape of a workpiece comes to be more complicated as well, therefore the shape of an abutting part of the workpiece with respect to a back gauge also comes to differ from each other in each bending process.
In mentioned conventional art, however, there is provided at the back gauge abutting part only one sensor, accordingly, for example, even if a workpiece is abutted against the back gauge with being slanted, the sensor is ON, thus to be regarded as in the suitable contact state.
As a result, due to that a workpiece is machined with being slanted, a defective product is produced, so that machining needs to be done again, and thus the efficiency of machining is extremely reduced and decreased.
Furthermore, to improve the efficiency of machining, there are some cases where a workpiece is abutted against a back gauge in the state in which the blade space between a punch and a die is made smaller.
However, owing to a small space between the blades, in mentioned conventional art, the contact state of a workpiece with respect to the back gauge cannot be visually observed by an operator, accordingly, the ON/OFF state of a sensor cannot be determined, and thus the contact state has to be determined only with the feel of hands, resulting in an extremely large burden of the operator.
(2) Second Problem
To solve such problem, the present application (in particular, Japanese Patent Application No. 2004-307854, applied on Oct. 22, 2004, which is one of three Japanese patent application of which the present application claims priority, and matured as U.S. Pat. No. 3,668,895 registered on Apr. 22, 2005) proposes a bending method and a machine thereof. However, at the time of pull back after a workpiece has been positioned, the misregistration of the workpiece may occur.
That is, as illustrated in FIG. 20, normally, after a workpiece W has been abutted against a back gauge abutting part 50 (FIG. 20 (A-1)) to be positioned, a ram is driven, when a punch (FIG. 20 (A-2)) has reached a pinching point PP, and this punch P is abutted against the workpiece W, and this workpiece W is clamped with the punch P and the die D.
In this state, the abutting part 50, to prevent interference accompanied by jumping of a workpiece W, is reversed (pull back), and by continuing to drive the ram, the workpiece W is bent with the punch P (FIG. 20 (A-3)) and the die D.
However, there is an error between an actual plate thickness t of a workpiece (FIG. 20 (B-1)) and a nominal plate thickness, for example, on the supposition of a thin plate thickness t, at a pinching point PP having been set (FIG. 20 (B-2)), the punch P is not abutted against the workpiece W, to be in the unclamped state.
Accordingly, when the abutting part 50 is reversed at the time of pull back, due to that an operator normally pushes the workpiece W to the abutting part 50, so that the workpiece W is reversed accompanied with the reverse of this abutting part 50 (FIG. 20(B-3)), and a bend line m is misaligned with the tip of the punch P, resulting in the occurrence of misregistration.
As a result, even if machining is made in the state of misregistration occurring (FIG. 20 (B-4)), the dimension H′ of a flange F to be formed will differ from the original dimension H, due to production of a detective product, machining has to be made again, thus leading to waste materials and increase of the cost of materials; as well as inspection processes after machining come to be necessary, an inspection time becomes longer, and thus, also in this respect, the efficiency of machining is extremely lowered.
Furthermore, since inspection processes after machining are required, the time of making discrimination between non-defective products and defective products is delayed, whereby the time of delivering non-defective products to intended destinations is delayed, and thus also at this point, resultingly, the entire efficiency of machining from the start of machining to the end thereof is reduced.
In addition, the present application (in particular, the above-mentioned JP 3,668,895) further proposes a bending machine provided with a plurality of contact confirmation sensors at one back gauge abutting part, which solves the mentioned initial problems (FIGS. 1 to 11 of the present application).
(3) Third Problem
According to this bending machine, the contact confirmation sensor that has to be ON in the case where a workpiece abutting part is suitably abutted against a back gauge abutting part has preliminarily been selected and specified, on the conditions of ON of this contact confirmation sensor having preliminarily been selected and specified, and ON of a foot pedal, a ram is driven, and a workpiece will be bent.
In the bending machine disclosed in mentioned U.S. Pat. No. 3,668,895, however, conventionally, there is no means with which an operator easily can select and specify the already-described contact confirmation sensor that has to be ON.
Consequently, like this, an operation panel with which an operator can easily make selection and specification has been desired to obtain.
(4) Fourth problem
Furthermore, the already-described conventional contact confirmation sensor is provided at a back gauge abutting part, and functions effectively in the case where a workpiece is abutted against the abutting face of the back gauge abutting part (FIG. 3 of mentioned U.S. Pat. No. 3,668,895 (FIG. 3 of the present application).
However, in the case where there is provided a workpiece support 3 for preventing this workpiece from being hung down when the workpiece is abutted (FIG. 34(A) of the present application), when the workpiece is abutted against this workpiece support 3 and has to be positioned (FIG. 34(B) of the present application), no conventional contact confirmation sensor effectively functions mechanically.
Consequently, a contact confirmation sensor effectively functioning even in the case where a workpiece is abutted against the workpiece support to be positioned has been desired to obtain.
Accordingly, a first object of the present invention is to provide a bending method and a machine thereof with which even if an abutting part of a workpiece with respect to a back gauge has any shape, by determination of whether or not this workpiece abutting part is suitably abutted against the back gauge abutting part, production of a defective product is prevented, thus the efficiency of machining is improved, as well as the burden of an operator is reduced.
Furthermore, a second object of the present invention is provide a bending method and a machine thereof with which by detection of defective products and non-defective products at the beginning, waste materials are eliminated to decrease the cost of materials, and inspection processes after machining are omitted to shorten an inspection time, as well as the appointed date of delivery of non-defective products is made earlier, thus resulting in improvement in the entire efficiency of machining.
Moreover, a third object of the present invention is to provide a bending machine including an operation panel with which in a bending machine provided with a plurality of contact confirmation sensors at one back gauge abutting part, the contact confirmation sensor that has to be ON in the case where a workpiece abutting part is suitably abutted against a back gauge abutting part can be easily selected and specified.
In addition, a fourth object of the present invention is to provide a bending machine including a contact confirmation sensor effectively functioning even in the case where in a bending machine provided with a plurality of contact confirmation sensors at one back gauge abutting part, a workpiece is abutted against a workpiece support to be positioned.